T. Sabri¹, L. Gavilan², C. Jäger¹, J. L. Lemaire², G. Vidali^2,5, H. Mutschke³ and T. Henning⁴

¹Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
²Observatoire de Paris/Université de Cergy-Pontoise, 5 mail Gay Lussac, F-95000 Cergy-Pontoise, France
³Laboratory Astrophysics Group of the Astrophysical Institute and University Observatory, Friedrich Schiller University Jena Schillergässchen 3, D-07743 Jena, Germany
⁴Max Planck Institute for Astronomy Königstuhl 17, D-69117 Heidelberg, Germany
⁵Physics Department, Syracuse University, Syracuse, NY 13244-1320, USA.

Amorphous, astrophysically relevant silicates were prepared by laser ablation of siliceous targets and subsequent quenching of the evaporated atoms and clusters in a helium/oxygen gas atmosphere. The described gas-phase condensation method can be used to synthesize homogeneous and astrophysically relevant silicates with different compositions ranging from nonstoichiometric magnesium iron silicates to pyroxene- and olivine-type stoichiometry. Analytical tools have been used to characterize the morphology, composition, and spectral properties of the condensates. The nanometer-sized silicate condensates represent a new family of cosmic dust analogs that can generally be used for laboratory studies of cosmic processes related to condensation, processing, and destruction of cosmic dust in different astrophysical environments. The well-characterized silicates comprising amorphous Mg₂SiO₄ and Fe₂SiO₄, as well as the corresponding crystalline silicates forsterite and fayalite, produced by thermal annealing of the amorphous condensates, have been used as real grain surfaces for H₂ formation experiments. A specifically developed ultra-high vacuum apparatus has been used for the investigation of molecule formation experiments. The results of these molecular formation experiments on differently structured Mg₂SiO₄ and Fe₂SiO₄ described in this paper will be the topic of the next paper of this series.

Reference
Sabri T, Gavilan L, Jäger C, Lemaire JL, Vidali G, Mutschke H and Henning T (2014) Interstellar Silicate Analogs for Grain-surface Reaction Experiments: Gas-phase Condensation and Characterization of the Silicate Dust Grains. The Astrophysical Journal Volume 780:180.
[doi:10.1088/0004-637X/780/2/180]

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Myriam Lemelin^1,2,*, Caroline-Emmanuelle Morisset³, Mickaël Germain¹, Victoria Hipkin³, Kalifa Goïta¹ and Paul G. Lucey⁴

¹Département de Géomatique Appliquée, Université de Sherbrooke, Sherbrooke, Québec, Canada
²Now at Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawai‘i at Manoa, Honolulu, Hawaii, USA
³Department of Space Exploration, Canadian Space Agency, Saint-Hubert, Québec, Canada
⁴Hawai‘i Institute of Geophysics and Planetology, Honolulu, Hawaii, USA

We model lunar ilmenite abundances over Mare Australe and Mare Ingenii regions using a new approach; we integrate Lunar Reconnaissance Orbiter Wide Angle Camera (WAC) and Clementine UV-visible/near-infrared (UVVIS/NIR) data to obtain a 14-band mosaic (320-2000 nm). We use Hapke’s radiative transfer equations to compute spectra for various mixtures of orthopyroxene, clinopyroxene, plagioclase, olivine, and ilmenite, with varying grain size, chemistry, and degree of maturity, and find the closest match between the modeled spectra and the spectra of the less mature pixels (optical maturity ≥ 0.2) in the 14-band mosaic. We calculate a “maximum stoichiometrically possible ilmenite content”, using Clementine-derived TiO₂ abundances and the amount of TiO₂ in stoichiometric ilmenite, and use it as a constraint in our model. We validate our methodology with lunar soil spectra of known composition. Our results show that the integrated WAC-UVVIS/NIR data and the UVVIS/NIR data overestimate ilmenite abundances by 8.80 wt % and 7.97 wt %, respectively, when a fixed maximum of 20 wt % ilmenite is used. When the maximum stoichiometrically possible ilmenite content is used as a constraint, the integrated WAC-UVVIS/NIR data give slightly more accurate ilmenite abundance estimation (±2.87 wt %) than when using only UVVIS/NIR data (± 3.04 wt %). We find ilmenite concentrations of 0−11 wt % in Mare Australe and 0−6 wt % in Mare Ingenii region. Ilmenite abundances between 4 and 7 wt % are exposed in Mare Australe, whereas ilmenite abundances between 7 and 11 wt % are found on the walls of 0.6-11.8 km diameter craters within Mare Australe.

Reference
Lemelin M, Morisset C-E, Germain M, Hipkin V, Goïta K and Lucey PG (in press) Ilmenite mapping of the lunar regolith over Mare Australe and Mare Ingenii regions: An optimized multisource approach based on Hapke radiative transfer theory. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004392]
Published by arrangement with John Wiley & Sons

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Adam J. McKay^a, Nancy J. Chanover^a, Michael A. DiSanti^b, Jeffrey P. Morgenthaler^c, Anita L. Cochran^d, Walter M. Harris^e and Neil Dello Russo^f

^aAstronomy Department, New Mexico State University, 1320 Frenger Mall, Las Cruces, NM 88001 (U.S.A.)
^bGoddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771 (U.S.A.)
^cPlanetary Science Institute, 1700 E. Fort Lowell, Ste 106, Tucson, AZ, 85719 (U.S.A)
^dUniverisity of Texas Austin/McDonald Observatory, 1 University Station, Austin, TX 78712, (U.S.A)
^eDepartment of Applied Science, University of California Davis, 1 Shields Ave., Davis, CA, 95616 (U.S.A)
^fJohns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD, 20723 (U.S.A.)

We present analysis of high spectral resolution optical spectra of comet 103P/Hartley taken during its Fall 2010 apparition. These spectra include transitions belonging to CN, C₂, CH, NH₂, and OI. We measure production rates and mixing ratios from these spectra. We find evidence for large changes in production rates (factors of a few) over the course of a nucleus rotation, in agreement with other measurements. We also measure variability with rotational phase in the CN/H₂O and C₂/CN ratios, which has not been previously reported for any comet. There may also be variability in the NH₂/H₂O ratio with rotational phase, but this trend is not as clear as for CN/H₂O. We interpret the changing mixing ratios as due to H₂O and C₂ being released primarily from the icy grain halo, while the CN parent molecule comes directly from the nucleus. There is evidence that the CH/CN ratio is higher pre-perihelion than post-perihelion. We conclude that the observed CN and NH₂ abundances are consistent with HCN and NH₃ being the dominant parent molecules for these species. The C₂ and CH abundances are higher than those of candidate parent molecules (C₂H₂ and CH₄respectively), so there must be another source for these molecules in 103P’s coma. Carbonaceous dust grains could serve as this source.

Reference
McKay AJ, Chanover NJ, DiSanti MA, Morgenthaler JP, Cochran AL, Harris WM and Russo ND (2013) Rotational Variation of Daughter Species Production Rates in Comet 103P/Hartley: Implications for the Progeny of Daughter Species and the Degree of Chemical Heterogeneity. Icarus 48:2441–2450.
[doi:10.1111/maps.12229]
Copyright Elsevier

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And will be back on the 27.12.2013

Cyrena Anne Goodrich^1,2,*, Allan H. Treiman³, Justin Filiberto⁴, Juliane Gross⁵, Michael Jercinovic²

¹Planetary Science Institute, Tucson, Arizona, USA
²Department of Geosciences, University of Massachusetts, Amherst, Massachusetts, USA
³Lunar and Planetary Institute, Houston, Texas, USA
⁴Department of Geology, Southern Illinois University, Carbondale, Illinois, USA
⁵Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA

We used new analytical and theoretical methods to determine the major and minor element compositions of the primary trapped liquid (PTLs) represented by melt inclusions in olivine and augite in the Martian clinopyroxenite, Nakhla, for comparison with previously proposed compositions for the Nakhla (or nakhlite) parent magma. We particularly focused on obtaining accurate K₂O contents, and on testing whether high K₂O contents and K₂O/Na₂O ratios obtained in previous studies of melt inclusions in olivine in Nakhla could have been due to unrepresentative sampling, systematic errors arising from electron microprobe techniques, late alteration of the inclusions, and/or boundary layer effects. Based on analyses of 35 melt inclusions in olivine cores, the PTL in olivine, PTL_oliv, contained (by wt) approximately 47% SiO₂, 6.3% Al₂O₃, 9.6% CaO, 1.8% K₂O, and 0.9% Na₂O, with K₂O/Na₂O = 2.0. We infer that the high K₂O content of PTL_oliv is not due to boundary layer effects and represents a real property of the melt from which the host olivine crystallized. This melt was cosaturated with olivine and augite. Its mg# is model-dependent and is constrained only to be ≥19 (equilibrium Fo = 40). Based on analyses of 91 melt inclusions in augite cores, the PTL in augite, PTL_aug, contained (by wt) 53–54% SiO₂, 7–8% Al₂O₃, 0.8–1.1% K₂O, and 1.1–1.4% Na₂O, with K₂O/Na₂O = 0.7–0.8. This K₂O content and K₂O/Na₂O ratio are significantly higher than inferred in studies of melt inclusions in augite in Nakhla by experimental rehomogenization. PTL_aug was saturated only with augite, and in equilibrium with augite cores of mg# 62. PTL_augrepresents the Nakhla parent magma, and does not evolve to PTL_oliv by fractional crystallization. We therefore conclude that olivine cores in Nakhla (and, by extension, other nakhlites) are xenocrystic. We propose that PTL_oliv and PTL_aug were generated from the same source region. PTL_oliv was generated first and emplaced to form olivine-rich cumulate rocks. Shortly thereafter, PTL_aug was generated and ascended through these olivine-rich cumulates, incorporating fragments of wallrock that became the xenocrystic olivine cores in Nakhla. The Nakhla (nakhlite) mantle source region was pyroxenitic with some olivine, and could have become enriched in K relative to Na via metasomatism. A high degree of melting of this source produced the silica-poor, alkali-rich magma PTL_oliv. Further ascension and decompression of the source led to generation of the silica-rich, relatively alkali-poor magma PTL_aug. Potassium-rich magmas like those involved in the formation of the nakhlites represent an important part of the diversity of Martian igneous rocks.

Reference
Goodrich CA, Treiman AH, Filiberto J, Gross J and Jercinovic M (2013) K2O-rich trapped melt in olivine in the Nakhla meteorite: Implications for petrogenesis of nakhlites and evolution of the Martian mantle. Meteoritics & Planetary Science 48:2371–2405.
[doi:10.1111/maps.12226]
Published by arrangement with John Wiley & Sons

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M. Ali-Dib¹, O. Mousis¹, G. S. Pekmezci², J. I. Lunine³, N. Madhusudhan⁴ and J.-M. Petit<sup>1

1</sup>Université de Franche-Comté, Institut UTINAM, CNRS/INSU, UMR 6213, Besançon Cedex, France
²Dipartimento di Astronomia, Universitá di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
³Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853, USA
⁴Department of Physics and Department of Astronomy, Yale University, New Haven, CT 06511, USA

Context. The observation of carbon-rich disks have motivated several studies questioning the influence of the C/O ratio on their gas phase composition in order to establish the connection between the metallicity of hot-Jupiters and that of their parent stars.
Aims. We propose a method that allows the characterization of the adopted C/O ratio in protoplanetary disks independently from the determination of the host star composition. Titanium and vanadium chemistries are investigated because they are strong optical absorbers and also because their oxides are known to be sensitive to the C/O ratio in some exoplanet atmospheres.
Methods. We use a commercial package based on the Gibbs energy minimization technique to compute the titanium and vanadium equilibrium chemistries in protoplanetary disks for C/O ratios ranging from 0.05 to 10. Our calculations are performed for pressures in the 10^-6–10^-2 bar domain, and for temperatures ranging from 50 K to 2000 K.
Results. We find that the vanadium nitride/vanadium oxide and titanium hydride/titanium oxide gas phase ratios strongly depend on the C/O ratio in the hot parts of disks (T ≥ 1000 K). Our calculations suggest that, in these regions, these ratios can be used as tracers of the C/O value in protoplanetary disks.

Reference
Ali-Dib M, Mousis O, Pekmezci GS, Lunine JI, Madhusudhan N and Petit J-M (2014) Influence of the C/O ratio on titanium and vanadium oxides in protoplanetary disks. Astronomy & Astrophysics 561:A60.
[doi:10.1051/0004-6361/201321780]
Reproduced with permission © ESO

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V. Alí-Lagoa^1,2, L. Lionni³, M. Delbo⁴, B. Gundlach⁵, J. Blum⁵ and J. Licandro^1,2

¹Instituto de Astrofísica de Canarias (IAC), c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
²Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
³University Paris VII – Diderot, 5 rue Thomas Mann, 75013 Paris, France
⁴UNS-CNRS-Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
⁵Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany

Aims. We derive the thermal inertia of 2008 EV₅, the baseline target for the Marco Polo-R mission proposal, and infer information about the size of the particles on its surface.
Methods. Values of thermal inertia were obtained by fitting an asteroid thermophysical model to NASA’s Wide-field Infrared Survey Explorer (WISE) infrared data. Grain size was derived from the constrained thermal inertia and a model of heat conductivity that accounts for different values of the packing fraction (a measure of the degree of compaction of the regolith particles).
Results. We obtain an effective diameter D = 370 ± 6   m, geometric visible albedo p_V = 0.13 ± 0.05 (assuming H = 20.0 ± 0.4), and thermal inertia Γ = 450 ± 60 J m^-2 s^−1/2 K^-1 at the 1σ level of significance for its retrograde spin-pole solution. The regolith particles radius is r = 6.6^+1.3_-1.3 mm for low degrees of compaction and r = 12.5^+2.7_-2.6 mm for the highest packing densities.

Reference
Alí-Lagoa V, Lionni L, Delbo M, Gundlach B, Blum J and Licandro J (2014) Thermophysical properties of near-Earth asteroid (341843) 2008 EV₅ from WISE data. Astronomy & Astrophysics 561:A45.
[doi:10.1051/0004-6361/201322215]
Reproduced with permission © ESO

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Álvaro Ribas^1,2,3, Bruno Merín⁴, Hervé Bouy² and Luke T. Maud⁵

¹European Space Astronomy Centre (ESA), PO Box 78, 28691 Villanueva de la Cañada Madrid Spain
²Centro de Astrobiología, INTA-CSIC, PO Box-Apdo. de correos 78, 28691 Villanueva de la Cañada Madrid, Spain
³Ingeniería y Servicios Aeroespaciales-ESAC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴Herschel Science Centre, ESAC-ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁵School of Physics & Astronomy, EC Stoner Building, University of Leeds, Leeds LS2 9JT, UK

Aims. We study the evolution of circumstellar disks in 22 young (1 to 100 Myr) nearby (within 500 pc) associations over the entire mass spectrum using photometry covering from the optical to the mid-infrared.
Methods. We compiled a catalog of 2340 spectroscopically-confirmed members of these nearby associations. We analyzed their spectral energy distributions and searched for excess related to the presence of protoplanetary disks. The dataset has been analyzed in a homogeneous and consistent way, allowing for meaningful inter-comparison of results obtained for individual regions. Special attention was given to the sensitivity limits and spatial completeness of the observations.
Results. We derive disk fractions as probed by mid-infrared excess in the 22 regions. The unprecedented size of our sample allows us to confirm the timescale of disk decay reported in the literature and to find new trends. The fraction of excess sources increases systematically if measured at longer wavelengths. Disk percentages derived using different wavelength ranges should therefore be compared with caution. The dust probed at 22–24 μm evolves slower than that probed at shorter wavelengths (3.4–12 μm). Assuming an exponential decay, we derive a timescale τ = 4.2 − 5.8 Myr at 22–24 μm for primordial disks, compared to 2 ~ 3 Myr at shorter wavelengths (3.4–12 μm). Primordial disks disappear around 10 ~ 20 Myr. Their decline matches in time a brief increase of the number of “evolved” disks (defined here as including transitional and debris disks). There is more dispersion in the fraction of excess sources with age when measured at 22–24 μm in comparison to shorter wavelengths.
Conclusions. The increase in timescale of excess decay at longer wavelength is compatible with inside-out disk clearing scenarios. The increased timescale of decay and larger dispersion in the distribution of disk fractions at 22–24 μm suggest that the inner (terrestrial-planet forming) and outer (giant-planet forming) zones evolve differently, the latter potentially following a variety of evolutionary paths. The drop of primordial disks and the coincident rise of evolved disks at 10 Myr are compatible with planet formation theories suggesting that the disappearance of the gas is immediately followed by the dynamical stirring of the disk.

Reference
Ribas A, Merín B, Bouy H and Maud LT (2014) Disk evolution in the solar neighbourhood – I. Disk frequencies from 1 to 100 Myr. Astronomy & Astrophysics 561:A54.
[doi:10.1051/0004-6361/201322597]
Reproduced with permission © ESO

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Kevin R. Grazier^a, Julie.C. Castillo-Rogez^a and Philip W. Sharp^b

^aJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
^bDepartment of Mathematics, University of Auckland, New Zealand

We quantify the relative contribution of volatiles supplied from outer Solar System planetesimal reservoirs to large wet asteroids during the first few My after the beginning of the Solar System. To that end, we simulate the fate of planetesimals originating within different regions of the Solar System–and thus characterized by different chemical inventories–using a highly accurate integrator tuned to handle close planet/planetesimal encounters. The fraction of icy planetesimals crossing the Asteroid Belt was relatively significant, and our simulations show that planetesimals originating from the Jupiter/Saturn region were orders of magnitude more abundant than those stemming from the Uranus and Neptune regions when the planets were just embryos. As the planets reached their full masses the Jupiter/ Saturn and Saturn/Uranus regions contributed similar fractions of planetesimals for any material remaining in these reservoirs late in the stage of planetary formation. This implies that large asteroids like Ceres accreted very little material enriched in low-eutectic volatiles (e.g., methanol, nitrogen and methane ices, etc.) and clathrate hydrates expected to condense at the very low temperatures predicted for beyond Saturn’s orbit in current early Solar nebula models. Further, a large fraction of the content in organics of Ceres and neighboring ice-rich objects originates from the outer Solar System.

Reference
Grazier KR, Castillo-Rogez JC and Sharp PW (in press) Dynamical Delivery of Volatiles to the Outer Main Belt. Icarus 780:154.
[doi:10.1088/0004-637X/780/2/154]
Copyright Elsevier

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Laura Vican¹ and Adam Schneider^2,3

¹Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
²Department of Physics and Astronomy, University of Georgia, Athens, GA 30602, USA
³Current Address: Department of Physics and Astronomy, The University of Toledo, Toledo, OH 43606, USA.

We used chromospheric activity to determine the ages of 2820 field stars. We searched these stars for excess emission at 22 μm with the Wide-Field Infrared Survey Explorer. Such excess emission is indicative of a dusty debris disk around a star. We investigated how disk incidence trends with various stellar parameters, and how these parameters evolve with time. We found 22 μm excesses around 98 stars (a detection rate of 3.5%). Of these 98 excess sources, 74 are presented here for the first time. We also measured the abundance of lithium in eight dusty stars in order to test our stellar age estimates.

Reference
Vican L and Schneider A (2014) The evolution of dusty debris disks around solar type stars. The Astrophysical Journal 780:154.
[doi:10.1088/0004-637X/780/2/154]

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